U.S. patent application number 14/200867 was filed with the patent office on 2015-02-05 for method and apparatus for adaptively setting threshold for signal demodulation.
This patent application is currently assigned to SAMSUNG ELECTRONICS CO., LTD.. The applicant listed for this patent is Samsung Electronics Co., Ltd.. Invention is credited to Chi Sung BAE, Chang Mok CHOI, Joon Seong KANG, Sang Joon KIM, Ui Kun KWON, Chang Soon PARK, Seung Keun YOON.
Application Number | 20150036768 14/200867 |
Document ID | / |
Family ID | 52427658 |
Filed Date | 2015-02-05 |
United States Patent
Application |
20150036768 |
Kind Code |
A1 |
KWON; Ui Kun ; et
al. |
February 5, 2015 |
METHOD AND APPARATUS FOR ADAPTIVELY SETTING THRESHOLD FOR SIGNAL
DEMODULATION
Abstract
Provided is a method and apparatus to adaptively set a threshold
for signal demodulation. The apparatus and the method include
adaptively setting a threshold to demodulate a currently received
symbol based on the demodulation value of a previously received
symbol based on a comparison value. The comparison value is
obtained by comparing a number of previously received symbols
having a demodulation value of "0" and a number of currently
received symbols having a demodulation value of "1".
Inventors: |
KWON; Ui Kun; (Hwaseong-si,
KR) ; PARK; Chang Soon; (Chungju-si, KR) ;
BAE; Chi Sung; (Yongin-si, KR) ; KANG; Joon
Seong; (Suwon-si, KR) ; KIM; Sang Joon;
(Hwaseong-si, KR) ; YOON; Seung Keun; (Seoul,
KR) ; CHOI; Chang Mok; (Seoul, KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Samsung Electronics Co., Ltd. |
Suwon-si |
|
KR |
|
|
Assignee: |
SAMSUNG ELECTRONICS CO.,
LTD.
Suwon-si
KR
|
Family ID: |
52427658 |
Appl. No.: |
14/200867 |
Filed: |
March 7, 2014 |
Current U.S.
Class: |
375/317 |
Current CPC
Class: |
H04L 27/06 20130101;
H04B 1/123 20130101 |
Class at
Publication: |
375/317 |
International
Class: |
H04B 1/12 20060101
H04B001/12 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 1, 2013 |
KR |
10-2013-0091381 |
Claims
1. A method, comprising: identifying a demodulation value of a
previously received symbol received during a predetermined symbol
period; and adaptively setting a threshold to demodulate a
currently received symbol based on the demodulation value of the
previously received symbol.
2. The method of claim 1, wherein the identifying comprises:
obtaining a comparison value by comparing a number of previously
received symbols having a demodulation value of "0" and a number of
currently received symbols having a demodulation value of "1".
3. The method of claim 2, wherein the obtaining comprises: setting
a weighted value based on a distance between the currently received
symbol and the previously received symbol; and comparing the number
of previously received symbols having the demodulation value of "0"
and the number of currently received symbols having the
demodulation value of "1" using the weighted value.
4. The method of claim 1, further comprising: alternately receiving
a training symbol having a demodulation value of "0" and a training
symbol having a demodulation value of "1" during a predetermined
training period.
5. The method of claim 4, wherein the adaptively setting comprises:
setting a fixed threshold using the training symbol having the
demodulation value of "0" and the training symbol having the
demodulation value of "1"; and setting the fixed threshold to be an
initial value of the threshold for demodulating the currently
received symbol.
6. The method of claim 4, wherein the adaptively setting comprises:
identifying an amplitude difference between the training symbol
having the demodulation value of "0" and the training symbol having
the demodulation value of "1"; and setting, using the amplitude
difference, a range in which the threshold to demodulate the
currently received symbol is to be changed.
7. The method of claim 2, wherein the adaptively setting comprises:
determining, based on the comparison value, an amount by which the
threshold for demodulating the currently received symbol is to be
changed.
8. The method of claim 7, wherein the identifying comprises:
calculating, using an exponential function based on the comparison
value, the amount by which the threshold to demodulate the
currently received symbol is to be changed.
9. The method of claim 8, wherein the calculating comprises:
calculating, by applying a Taylor series to the exponential
function based on the comparison value, the amount by which the
threshold to demodulate the currently received symbol is to be
changed.
10. An apparatus, comprising: a demodulation value identifier
configured to identify a demodulation value of a previously
received symbol received during a predetermined symbol period; and
a threshold setting unit configured to adaptively set a threshold
to demodulate a currently received symbol based on the demodulation
value of the previously received symbol.
11. The apparatus of claim 10, further comprising: a buffer
configured to store the previously received symbol and the
currently received symbol, wherein the demodulation value
identifier and the threshold setting unit receive the previously
received symbol and the currently received symbol.
12. The apparatus of claim 10, wherein the demodulation value
identifier comprises: a comparison value obtainer configured to
obtain a comparison value by comparing a number of the previously
received symbols having a demodulation value of "0" and a number of
the currently received symbols having a demodulation value of
"1".
13. The apparatus of claim 10, wherein the comparison value
obtainer comprises: a weighted value setting unit configured to set
a weighted value based on a distance between the currently received
symbol and the previously received symbol; and a symbol number
comparator configured to compare the number of previously received
symbols having the demodulation value of "0" and the number of
currently received symbols having the demodulation value of "1"
using the weighted value.
14. The apparatus of claim 10, further comprising: a training
symbol receiver configured to alternately receive a training symbol
having a demodulation value of "0" and a training symbol having a
demodulation value of "1" during a predetermined training
period.
15. The apparatus of claim 14, wherein the threshold setting unit
comprises: a fixed threshold setting unit configured to set a fixed
threshold using the training symbol having the demodulation value
of "0" and the training symbol having the demodulation value of
"1"; and an initial value setting unit configured to set the fixed
threshold to be an initial value of the threshold to demodulate the
currently received symbol.
16. The apparatus of claim 14, wherein the threshold setting unit
comprises: an amplitude difference identifier configured to
identify an amplitude difference between the training symbol having
the demodulation value of "0" and the training symbol having the
demodulation value of "1"; and a range setting unit configured to
set, using the amplitude difference, a range in which the threshold
to demodulate the currently received symbol is to be changed.
17. The apparatus of claim 12, wherein the threshold setting unit
comprises: an amount determiner configured to determine, based on
the comparison value, an amount by which the threshold to
demodulate the currently received symbol is to be changed.
18. A method, comprising: calculating, prior to demodulating a
currently received signal, an amount of threshold to be changed
based on at least one of a demodulation value of "0" and a
demodulation value of "1" among demodulation signals occurring in a
predetermined period; and demodulating the currently received
signal based on the calculated amount of threshold to be
changed.
19. The method of claim 18, wherein the calculating comprises:
obtaining a comparison value by comparing a number of previously
received signals having the demodulation value of "0" and a number
of currently received signals having the demodulation value of
"1".
20. The method of claim 19, wherein the calculating further
comprises: calculating, using an exponential function based on the
comparison value, the amount by which the threshold to demodulate a
currently received signal is to be changed.
21. The method of claim 20, wherein the calculating, using the
exponential function, further comprises: calculating, by applying a
Taylor series to the exponential function based on the comparison
value, the amount by which the threshold to demodulate the
currently received signal is to be changed.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims the benefit under 35 U.S.C.
.sctn.119(a) of Korean Patent Application No. 10-2013-0091381,
filed on Aug. 1, 2013, in the Korean Intellectual Property Office,
the entire disclosure of which is incorporated herein by reference
for all purposes.
BACKGROUND
[0002] 1. Field
[0003] The following description relates to a method and apparatus
to adaptively set a threshold for signal demodulation.
[0004] 2. Description of Related Art
[0005] A sensor network is rapidly becoming widespread based on
fast improvement and commercialization of wireless network
technology. Wireless network technology standardization is being
actively conducted by the Institute of Electrical and Electronics
Engineers (IEEE) through, for example, IEEE 802.15.4, which is a
standard that specifies a physical layer and media access control
for low-rate wireless personal area networks (LR-WPANs). In
particular, standardization of Bluetooth and ZigBee is also being
performed.
[0006] A wireless sensor device may be applied to various fields,
for example, home security, medicine, mobile healthcare, chemical
and biological defect monitoring, breakdown and damage diagnosis
for machinery, environmental monitoring, sensing information
associated with natural disasters, intelligent logistics
management, real-time security, and remote observation.
[0007] Various wireless sensor networks and local area networks
(LANs) require compact-sized sensors. Also, for a durable operation
of a number of sensors, it is advantageous for wireless sensors to
consume less power and have low complexity requirements.
[0008] In particular, in a wireless body area network (WBAN), a
sensor to be attached to a human body needs to have low power and
low complexity requirements. When attached to a human body, the
sensor communicates wirelessly with an adjacent mobile device or a
sensor of another human body.
[0009] Recently, to improve a performance of a super-low power
analog circuit, research on stable demodulation of a received
signal has increased.
SUMMARY
[0010] This Summary is provided to introduce a selection of
concepts in a simplified form that are further described below in
the Detailed Description. This Summary is not intended to identify
key features or essential features of the claimed subject matter,
nor is it intended to be used as an aid in determining the scope of
the claimed subject matter.
[0011] In accordance with one configuration, there is provided a
method, including identifying a demodulation value of a previously
received symbol received during a predetermined symbol period; and
adaptively setting a threshold to demodulate a currently received
symbol based on the demodulation value of the previously received
symbol.
[0012] The identifying may include obtaining a comparison value by
comparing a number of previously received symbols having a
demodulation value of "0" and a number of currently received
symbols having a demodulation value of "1".
[0013] The obtaining may include setting a weighted value based on
a distance between the currently received symbol and the previously
received symbol; and comparing the number of previously received
symbols having the demodulation value of "0" and the number of
currently received symbols having the demodulation value of "1"
using the weighted value.
[0014] The method may also include alternately receiving a training
symbol having a demodulation value of "0" and a training symbol
having a demodulation value of "1" during a predetermined training
period.
[0015] The adaptively setting may include setting a fixed threshold
using the training symbol having the demodulation value of "0" and
the training symbol having the demodulation value of "1"; and
setting the fixed threshold to be an initial value of the threshold
for demodulating the currently received symbol.
[0016] The adaptively setting may include identifying an amplitude
difference between the training symbol having the demodulation
value of "0" and the training symbol having the demodulation value
of "1"; and setting, using the amplitude difference, a range in
which the threshold to demodulate the currently received symbol is
to be changed.
[0017] The adaptively setting may include determining, based on the
comparison value, an amount by which the threshold for demodulating
the currently received symbol is to be changed.
[0018] The identifying may include calculating, using an
exponential function based on the comparison value, the amount by
which the threshold to demodulate the currently received symbol is
to be changed.
[0019] The calculating may include calculating, by applying a
Taylor series to the exponential function based on the comparison
value, the amount by which the threshold to demodulate the
currently received symbol is to be changed.
[0020] In accordance with another illustrative configuration, there
is provided an apparatus, including a demodulation value identifier
configured to identify a demodulation value of a previously
received symbol received during a predetermined symbol period; and
a threshold setting unit configured to adaptively set a threshold
to demodulate a currently received symbol based on the demodulation
value of the previously received symbol.
[0021] The apparatus may also include a buffer configured to store
the previously received symbol and the currently received symbol,
wherein the demodulation value identifier and the threshold setting
unit receive the previously received symbol and the currently
received symbol.
[0022] The demodulation value identifier may include a comparison
value obtainer configured to obtain a comparison value by comparing
a number of the previously received symbols having a demodulation
value of "0" and a number of the currently received symbols having
a demodulation value of "1".
[0023] The comparison value obtainer may include a weighted value
setting unit configured to set a weighted value based on a distance
between the currently received symbol and the previously received
symbol; and a symbol number comparator configured to compare the
number of previously received symbols having the demodulation value
of "0" and the number of currently received symbols having the
demodulation value of "1" using the weighted value.
[0024] The apparatus may also include a training symbol receiver
configured to alternately receive a training symbol having a
demodulation value of "0" and a training symbol having a
demodulation value of "1" during a predetermined training
period.
[0025] The threshold setting unit may also include a fixed
threshold setting unit configured to set a fixed threshold using
the training symbol having the demodulation value of "0" and the
training symbol having the demodulation value of "1"; and an
initial value setting unit configured to set the fixed threshold to
be an initial value of the threshold to demodulate the currently
received symbol.
[0026] The threshold setting unit may include an amplitude
difference identifier configured to identify an amplitude
difference between the training symbol having the demodulation
value of "0" and the training symbol having the demodulation value
of "1"; and a range setting unit configured to set, using the
amplitude difference, a range in which the threshold to demodulate
the currently received symbol is to be changed.
[0027] The threshold setting unit may include an amount determiner
configured to determine, based on the comparison value, an amount
by which the threshold to demodulate the currently received symbol
is to be changed.
[0028] In accordance with a configuration, there is provided
method, including calculating, prior to demodulating a currently
received signal, an amount of threshold to be changed based on at
least one of a demodulation value of "0" and a demodulation value
of "1" among demodulation signals occurring in a predetermined
period; and demodulating the currently received signal based on the
calculated amount of threshold to be changed.
[0029] The calculating may include obtaining a comparison value by
comparing a number of previously received signals having the
demodulation value of "0" and a number of currently received
signals having the demodulation value of "1".
[0030] The calculating may include calculating, using an
exponential function based on the comparison value, the amount by
which the threshold to demodulate a currently received signal is to
be changed.
[0031] The calculating, using the exponential function, may include
calculating, by applying a Taylor series to the exponential
function based on the comparison value, the amount by which the
threshold to demodulate the currently received signal is to be
changed.
[0032] Other features and aspects may be apparent from the
following detailed description, the drawings, and the claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0033] These and/or other aspects will become apparent and more
readily appreciated from the following description of the
embodiments, taken in conjunction with the accompanying drawings in
which:
[0034] FIG. 1 illustrates an example of a conventional
super-regenerative receiver.
[0035] FIG. 2 illustrates an example of an input signal, a damping
function, and an output signal of a super-regenerative receiver, in
accordance with an embodiment.
[0036] FIG. 3 illustrates an example of an analog-to-digital
converter (ADC) output waveform with respect to a received signal
of a super-regenerative receiver, in accordance with an
embodiment.
[0037] FIGS. 4A and 4B illustrate an example of a received symbol
demodulation scheme, in accordance with an embodiment.
[0038] FIG. 5 illustrates an example of a method to adaptively set
a threshold, in accordance with an embodiment.
[0039] FIG. 6 illustrates an example of a fixed threshold in a
method to adaptively set a threshold, in accordance with an
embodiment.
[0040] FIG. 7 illustrates an example of a threshold to demodulate a
currently received symbol, in accordance with an embodiment.
[0041] FIG. 8 illustrates an example of an apparatus to set a
threshold, in accordance with an embodiment.
[0042] Throughout the drawings and the detailed description, unless
otherwise described, the same drawing reference numerals will be
understood to refer to the same elements, features, and structures.
The relative size and depiction of these elements may be
exaggerated for clarity, illustration, and convenience.
DETAILED DESCRIPTION
[0043] The following detailed description is provided to assist the
reader in gaining a comprehensive understanding of the methods,
apparatuses, and/or systems described herein. Accordingly, various
changes, modifications, and equivalents of the methods,
apparatuses, and/or systems described herein will be suggested to
those of ordinary skill in the art. The progression of processing
steps and/or operations described is an example; however, the
sequence of and/or operations is not limited to that set forth
herein and may be changed as is known in the art, with the
exception of steps and/or operations necessarily occurring in a
certain order. Also, description of well-known functions and
constructions may be omitted for increased clarity and
conciseness.
[0044] There is a need for sensor devices to be installed in a
wireless sensor network and a local area network (LAN) to be
designed in a compact size, and a low power and low complexity
structure.
[0045] In general, a superheterodyne radio frequency (RF)
structured receiver may use an intermediate frequency band to
improve performance, for example, sensitivity, rather than
converting a received signal from a high-frequency band directly to
a base band. However, complexity, costs, and power consumption may
increase.
[0046] In an RF portion, a modem technology based on a
superheterodyne RF structure scheme requires a greater amount of
power when compared to a digital base band portion. For example, in
a case of a modem chip for a low power wireless personal area
network (WPAN), a digital signal processing portion may use
approximately 0.5 milliwatts (mW) of power for transmission and
reception, whereas an analog signal processing portion may use
power of approximately 21 mW in a reception mode and 30 mW in a
transmission mode.
[0047] Accordingly, research on reducing power consumption of
communication modems is being actively conducted using various low
power RF structured receiver. In particular, a receiver structure
using a super-regenerative receiver is designed to amplify an
output signal and detect a signal using a positive feedback
structure. Because a simple RF structured receiver using a
relatively fewer number of active devices is adopted, the RF
structured receiver attracts a lot of attention as an ultra low
power receiver.
[0048] Although a short distance transmitting and receiving system
adopting the low power and low complexity RF structured receiver
significantly reduces power consumption, performance degradation of
the analog signal processing portion may cause overall performance
degradation in the system.
[0049] The super-regenerative receiver may experience performance
degradation in a system due to a low selectivity characteristic of
a frequency response.
[0050] FIG. 1 illustrates an example of a conventional
super-regenerative receiver.
[0051] Referring to FIG. 1, an RF signal passes through a low noise
amplifier (LNA) 110 and subsequently an RF oscillator 120. In this
instance, the RF oscillator 120 may be, for example, a
super-regenerative oscillator (SRO). The RF oscillator 120
amplifies the RF signal corresponding to a predetermined frequency
using a positive feedback loop. As the amplification continues, an
oscillation may occur. Thus, a configuration to stop the
oscillation is required. A quench oscillator 140 may control
periodical generation and terminate the oscillation. For example,
in a case in which an on-off keying (OOK) modulation scheme is
used, when a transmitting end transmits a signal corresponding to a
transmission symbol "1", the RF oscillator 120 may generate a
relatively strong oscillation signal controlled by the quench
oscillator 140.
[0052] When the transmitting end transmits a signal corresponding
to a transmission symbol "0", the RF oscillator 120 may generate,
in practice, a weak oscillation signal due to noise, although ideal
oscillation is absent.
[0053] An RF signal input to the RF oscillator 120, an output
signal, and a damping function of a closed-loop system using the
positive feedback loop is illustrated in FIG. 2.
[0054] An envelope detector 130 detects an envelope from the output
signal of the RF oscillator 120. A low-pass filter (LPF) 150
filters a predetermined area in the detected envelope.
[0055] In this example, the output signal may require a
high-magnitude of amplification for detection in a digital base
band because an output signal of the envelope detector 130 may be a
weak signal. Also, controlling a magnitude of amplification as a
function of a distance between a transmitter and a receiver may be
necessary in the envelope detected from the output signal at the
envelope detector 130. Thus, the envelope detected from the output
signal at the envelope detector 130 passes through a variable gain
amplifier (VGA) 160, which is configured to amplify a signal by
controlling a magnitude of amplification.
[0056] In this instance, the VGA 160 amplifies a received signal
from the LPF 150 to have an intensity of at least 40 decibels (dB).
When the envelope detected from the output signal at the envelope
detector 130 includes a direct current (DC) offset component, a
signal over-amplified due to the DC offset component may saturate
an entire circuit.
[0057] In particular, when an OOK demodulation signal passes
through the envelope detector 130, the envelope detected from the
output signal always having a positive value may be obtained.
[0058] The signal amplified by the VGA 160 may pass through an
analog-to-digital converter (ADC) 170, and be provided to a
physical layer (PHY) (not shown).
[0059] FIG. 2 illustrates an example of an input signal, a damping
function, and an output signal of a super-regenerative receiver, in
accord with an embodiment.
[0060] Referring to FIG. 2, in response to an RF signal v(t) input
to an SRO, an output signal v.sub.o(t) of the SRO is provided in a
form of an RF pulse series in which oscillation and attenuation are
periodically repeated for each quench period T.sub.q.
[0061] Here, .zeta.(t) refers to a damping function of a
closed-loop system .zeta.(t) varies in response to a signal of a
quench oscillator. When a value of .zeta.(t) changes from a
positive value to a negative value, an SRO output signal may
initiate oscillation, and an unstable interval may start, in which
an amplitude value gradually increases. The unstable interval may
continue until the value of .zeta.(t) changes from a negative value
to a positive value. When the amplitude value reaches a maximum
value, a stable interval may begin, in which the amplitude value
attenuates.
[0062] An RF pulse occurring in an SRO output during a single
quench period may reoccur during a subsequent quench period. The RF
pulse occurring in the SRO output may overlap another RF pulse
newly generated during the subsequent quench period, and cause an
occurrence of intersymbol interference (ISI). In one example, the
occurrence of the ISI is referred to as a hangover effect. To
eliminate the hangover effect, .zeta.(t) may have a value of
.zeta..sub.dc corresponding to a DC component value.
[0063] As the amplitude value of the RF input signal v(t)
increases, the amplitude value of the SRO output v.sub.o(t) may
also increase.
[0064] A regenerative gain is a main factor in determining the
amplitude value of the SRO output v.sub.o(t). The regenerative gain
may be determined based on integral values of a sensitive curve and
a normalized envelope of the RF signal input to the SRO.
[0065] Referring to the following equations, when the RF input
signal of the SRO corresponds to
v(t)=Vp.sub.c(t)cos(.omega..sub.0t+.phi.), the SRO output
v.sub.o(t) may be calculated as follows.
v.sub.o(t)=VK.sub.0K.sub.gK.sub.rp(t)cos(.omega..sub.0t+.phi.)
K.sub.r-.zeta..sub.0.omega..sub.0.intg..sub.t.sup.a.sup.t.sup.bp.sub.c(.-
tau.)s(.tau.)d.tau.
s(t)=exp(.omega..sub.0.intg..sub.0.sup.t.zeta.(.lamda.)d.lamda.)
p(t)-exp(-.omega..sub.0.intg..sub.t.sup.b.sup.t.zeta.(.lamda.)d.lamda.)
[0066] In one example, p.sub.c(t) denotes a pulse envelope of which
a maximum value is normalized to "1". K.sub.r denotes the
regenerative gain, s(t) denotes the sensitivity curve, and p(t)
denotes the normalized envelope of the SRO output.
[0067] An amplitude of the SRO output is determined based on a
value of V corresponding to a peak amplitude of the RF input
signal, and integral values of s(t) and p.sub.c(t).
[0068] An increase of the peak amplitude of the RF input signal may
cause an increase of the peak amplitude of the SRO output, and the
peak amplitude of the SRO output may be also determined based on an
amount of input energy captured based on an overlap level of s(t)
and p.sub.c(t).
[0069] FIG. 3 illustrates an example of an output waveform of an
ADC with respect to a received signal of a super-regenerative
receiver, in accord with an embodiment.
[0070] Referring to FIG. 3, when the super-regenerative receiver
receives a predetermined transmission signal modulated using an
OOK, the ADC may obtain an output waveform with a dynamic range
from "0" to "255", using 8-bit of resolution bit.
[0071] In one example, the output signal of an envelope detector
always has a positive value. Thus, a VGA may be designed to have a
frequency response characteristic to eliminate or restrict a low
frequency component to eliminate a DC offset component and maintain
a low power.
[0072] Accordingly, an output signal of the VGA may have an average
value of "0" and a waveform alternating between a positive value
and a negative value centered around the average value of "0" may
be provided.
[0073] Due to a characteristic of mitigating a DC offset, when an
identical signal selected from transmission symbols "0" and "1" is
alternately received, an output signal of the ADC may not maintain
an amplitude of a predetermined transmission signal and may have a
tendency 310 to approach an average value, for example, zero volts.
In one example, the zero volts may be an ADC of level 128.
[0074] In terms of a long time period, the DC offset component may
be eliminated. However, a DC fluctuation effect, in which a DC
offset value changes based on a time during a time period on a
signal-by-signal basis, may occur depending on whether a
predetermined transmission signal occurs alternately.
[0075] In a case of an OOK modulation and demodulation scheme,
setting a threshold for determining whether a signal is present may
have a strong influence on a bit error rate performance.
[0076] Accordingly, mitigating a DC offset may distort the output
signal of the ADC, for example, an input value of a digital base
band and; thus, cause performance degradation in the bit error
rate.
[0077] FIGS. 4A and 4B illustrate an example of a received symbol
demodulation scheme, in accord with an embodiment.
[0078] Referring to FIGS. 4A and 4B, a super-regenerative receiver
receives a symbol and demodulates the received symbol. As
illustrated in FIG. 4A, the super-regenerative receiver receives a
single symbol during one bit period and demodulates the received
symbol using a threshold. For example, when the super-regenerative
receiver alternately receives a symbol having a symbol value of "0"
and a symbol having a symbol value of "1", the super-regenerative
receiver may set the threshold to be an intermediate value between
"0" and "1".
[0079] FIG. 4B illustrates a scheme to determine a demodulation
value of a received symbol by comparing the received symbol and the
threshold. When the received symbol is less than the threshold, for
example, B.sub.n<thr, a demodulation value {circumflex over
(d)}.sub.n may be determined to be "0". When the received symbol is
greater than the threshold, for example, B.sub.n>thr, the
demodulation value {circumflex over (d)}.sub.n may be determined to
be "1".
[0080] FIG. 5 illustrates an example of a method of adaptively
setting a threshold, in accord with an embodiment.
[0081] Referring to FIG. 5, in operation 510, the method identifies
a demodulation value of a previously received symbol received
during a predetermined symbol period. In one example, the
previously received symbol is a symbol received prior to a
currently received symbol. The predetermined symbol period
indicates a period of time in which the previously received symbol
is received. A length of the predetermined symbol period may vary
based on a system of the super-regenerative receiver.
[0082] In operation 510, the method also compares a number of
previously received symbols having a demodulation value of "0" with
a number of previously received symbols having a demodulation value
of "1". A comparison value may be obtained based on a result of the
comparing. For example, when the length of the predetermined symbol
period is "8", the number of previously received symbols having the
demodulation value of "0" is "3", and the number of previously
received symbols having the demodulation value of "1" is "5", the
comparison value may be "2".
[0083] Due to an AC coupling effect, a DC fluctuation effect may
vary based on a distance between the currently received symbol and
the previously received symbol. For example, a DC fluctuation
effect in a case in which two previously received symbols
correspond to (1,0) may differ from a DC fluctuation effect in a
case in which two previously received symbols correspond to
(0,1).
[0084] To reflect the DC fluctuation effect, the comparison value
may be set in operation 510, using a weighted value. As an example,
in operation 510, the weighted value may be set based on a distance
between the currently received symbol and the previously received
symbol. Also, in operation 510, the number of previously received
symbols having the demodulation value of "0" may be compared to the
previously received symbols having the demodulation value of "1",
and the comparison value may be set based on a result of the
comparing.
[0085] The comparison value may be expressed as an equation of
i = 1 M ( 2 .times. d ^ n - i - 1 ) . ##EQU00001##
In one example, M denotes the length of the predetermined symbol
period, and {circumflex over (d)}.sub.n-i denotes a demodulation
value of (n-i).sup.th symbol having a value of "0" of "1". Using an
equation of 2.times.{circumflex over (d)}.sub.n-i-1, the previously
received symbol having the demodulation value of "0" may be
expressed as "-1", and the previously received symbol having the
demodulation value of "1" may be expressed as "1". Accordingly, the
comparison value obtained by comparing the number of previously
received symbols having the demodulation value of "0" and the
number of previously received symbols having the demodulation value
of "1" may be expressed as equation
i = 1 M ( 2 .times. d ^ n - i - 1 ) . ##EQU00002##
For example, the comparison value of "3" may indicate that the
number of previously received symbols having the demodulation value
of "1" is greater than the number of previously received symbols
having the demodulation value of "0" by "3". The comparison value
of "-2" may indicate that the number of previously received symbols
having the demodulation value of "0" is greater than the number of
previously received symbols having the demodulation value of "1" by
"2".
[0086] When the weighted value based on the distance between the
currently received symbol and the previously received symbol is
applied to the comparison value, the comparison value is expressed
by the following equation
i = 1 M w i ( 2 .times. d ^ n - i - 1 ) . ##EQU00003##
In one example, W.sub.i is a weighted value of i.sup.th symbol. For
example, five previously received symbols correspond to (0, 0, 1,
1, 1), the comparison value without applying the weighted value is
"1". However, when the weighted values based on the distance
between the currently received symbol and the previously received
symbol correspond to (0.6, 0.7, 0.8, 0.9, 1), the comparison value
applied the weighted value may be "1.4".
[0087] In operation 520, the method adaptively sets the threshold
for demodulating the currently received symbol based on the
demodulation value of the previously received symbol.
[0088] As described above, when the symbol having the demodulation
value of "1" or the symbol having the demodulation value of "0" is
continuously received, an output signal of the ADC may not maintain
an amplitude in the symbol and may tend to maintain an average
value. Thus, to obtain an optimized performance, the threshold to
demodulate the currently received symbol may identically vary as
the varying output signal of the ADC. Accordingly, in operation
520, the method adaptively sets the threshold by obtaining a range
in which the threshold is to be changed, an amount by which the
threshold is to be changed, and an initial value of the
threshold.
[0089] To set the range and the initial value of the threshold, a
training symbol having a demodulation value of "0" and a training
symbol having a demodulation value of "1" may be alternately
received during a predetermined training period. When the training
symbol having the demodulation value of "0" and the training symbol
having the demodulation value of "1" are alternately received
during the predetermined training period, probability distribution
of the training symbol having the demodulation value of "0" may be
identical to probability distribution of the training symbol having
the demodulation value of "1". Accordingly, a fixed threshold may
be set to be an intermediate value between "0" and "1". Because the
fixed threshold is set to be the intermediate value between "0" and
"1", the amount by which the threshold to demodulate the currently
received symbol is to be changed, which will be described
hereinafter, is based on the comparison value obtained by comparing
the number of previously received symbols having the demodulation
value of "0" to the number of previously received symbols having
the demodulation value of "1". Because the fixed threshold may be
set to be another value, an amount by which the threshold for
demodulating the currently received symbol is to be changed may be
based on another parameter, in lieu of the comparison value. For
example, when the fixed threshold is set to be the other value in
lieu of the intermediate value between "0" and "1", the range in
which the threshold to demodulate the currently received symbol is
to be changed is based on the number of previously received symbols
having the demodulation value of "0" and the number of previously
received symbols having the demodulation value of "1".
[0090] The fixed threshold is set to be the initial value of the
threshold to demodulate the currently received symbol, and the
threshold for demodulating the currently received symbol may vary
based on the initial value.
[0091] In operation 520, the method identifies an amplitude
difference between the training symbol having the demodulation
value of "0" and the training symbol having the demodulation value
of "1" during the predetermined training period. The range in which
the threshold to demodulate the currently received symbol is to be
changed is set using the identified amplitude difference. The range
in which the threshold for demodulating the currently received
threshold is to be changed may vary based on characteristics of a
system. For example, when the probability distribution of the
training symbol has the demodulation value of "0" and is identical
to the probability distribution of the training symbol having the
demodulation value of "1", the amplitude difference between the
probability distribution of the training symbol having the
demodulation value of "0" and the probability distribution of the
training symbol having the demodulation value of "1" are identified
using sig_pwr and the range in which the threshold for demodulating
the currently received symbol is to be changed is set as
sig_pwr 2 . ##EQU00004##
Thus, the range in which the threshold to demodulate the currently
received symbol is changed may be limited by
sig_pwr 2 . ##EQU00005##
[0092] In operation 520, the method determines the amount by which
the threshold for demodulating the currently received symbol is to
be changed based on the comparison value. The method changes the
amount by which the threshold to demodulate the currently received
symbol based on a magnitude of the comparison value and whether the
comparison value is a positive value or a negative value.
[0093] In particular, the method calculates the amount by which the
threshold to demodulate the currently received symbol is to be
changed using an exponential function based on the comparison
value. The threshold for demodulating the currently received symbol
may be expressed as Equation 1.
If i = 1 M ( 2 .times. d ^ n - i - 1 ) > 0 thr_amt n = thr_fix +
sig_pwr 2 .times. ( - .tau. c .times. ( i = 1 M ( 2 .times. d ^ n -
i - 1 ) ) - 1 ) else , thr_amt n = thr_fix + sig_pwr 2 .times. ( 1
- .tau. c .times. ( i = 1 M ( 2 .times. d ^ n - i - 1 ) ) ) [
Equation 1 ] ##EQU00006##
[0094] In one example, thr_amt.sub.n denotes a threshold to
demodulate n.sup.th received symbol and thr_fix denotes a fixed
threshold.
sig_pwr 2 ##EQU00007##
denotes half of the amplitude difference between the training
symbol having the demodulation value of "0" and the training symbol
having the demodulation value of "1", and indicates the range in
which the threshold to demodulate the currently received symbol is
to be changed. .tau..sub.c corresponds to a time constant used to
control the amount by which the threshold to demodulate the
currently received symbol is to be changed. .tau..sub.c varies
based on a system of a super-regenerative receiver
i = 1 M ( 2 .times. d ^ n - i - 1 ) ##EQU00008##
denotes the comparison value.
[0095] When the comparison value is greater than "0", or when the
number of currently received symbols having the demodulation value
of "1" is greater than the number of currently received symbols
having the demodulation value of "0", the threshold to demodulate
the currently received symbol varies based on
thr_fix + sig_pwr 2 .times. ( - .tau. c .times. ( i = 1 M ( 2
.times. d ^ n - i - 1 ) ) - 1 ) . ##EQU00009##
The threshold to demodulate the currently received symbol varies,
based on
( - .tau. c .times. ( i = 1 M ( 2 .times. d ^ n - i - 1 ) ) - 1 ) ,
##EQU00010##
using the fixed threshold as the initial value and
sig_pwr 2 ##EQU00011##
as the range in which the threshold is to be changed. As the
comparison value increases, the threshold to demodulate the
currently received symbol converges on a difference value between
thr_fix and
sig_pwr 2 . ##EQU00012##
[0096] When the comparison value is less than "0", or when the
number of previously received symbols having the demodulation value
of "0" is greater than previously received symbols having the
demodulation value of "1", the threshold to demodulate the
currently received symbol varies based on
thr_fix + sig_pwr 2 .times. ( 1 - .tau. c .times. ( i = 1 M ( 2
.times. d ^ n - i - 1 ) ) ) . ##EQU00013##
As the comparison value decreases, or as the number of previously
received symbols having the demodulation value of "0" becomes
greater than previously received symbols having the demodulation
value of "1", the threshold to demodulate the currently received
symbol converges on a sum of thr_fix and
sig_pwr 2 . ##EQU00014##
[0097] In addition, when the weighted value based on a distance
between the currently received symbol and the previously received
symbol is applied to the comparison value, the threshold to
demodulate the currently received symbol is expressed as Equation
2.
If i = 1 M ( 2 .times. d ^ n - i - 1 ) > 0 thr_amt n = thr_fix +
sig_pwr 2 .times. ( - .tau. c .times. ( i = 1 M w i ( 2 .times. d ^
n - i - 1 ) ) - 1 ) else , thr_amt n = thr_fix + sig_pwr 2 .times.
( 1 - .tau. c .times. ( i = 1 M w i ( 2 .times. d ^ n - i - 1 ) ) )
[ Equation 2 ] ##EQU00015##
[0098] In one example, W.sub.i denotes a weighted value of an
i.sup.th symbol. As described in Equation 2, when the weighted
value based on the distance between the currently received symbol
and the previouly received symbol is applied to the comparison
value, the DC fluctuation effect may be more accurately
reflected.
[0099] As described in Equation 3 and Equation 4 below, the amount
by which the threshold to demodulate the currently received symbol
is to be changed may be approximately expressed by applying a first
order Taylor series to an exponential function based on the
comparison value. In an example, Equation 4 illustrates a case in
which the weighted value based on the distance between the
currently received symbol and the previously received symbol is
applied to the comparison value.
thr_amt n .apprxeq. thr_fix + sig_pwr 2 .times. ( - .tau. c .times.
( i = 1 M ( 2 .times. d ^ n - i - 1 ) ) ) [ Equation 3 ] thr_amt n
.apprxeq. thr_fix + sig_pwr 2 .times. ( - .tau. c .times. ( i = 1 M
w i ( 2 .times. d ^ n - i - 1 ) ) ) [ Equation 4 ] ##EQU00016##
[0100] Based on Equation 3 and Equation 4, the amount to be changed
of the threshold to demodulate the currently received symbol may be
expressed as a single equation irrespective of a sign of the
comparison value. Accordingly, a system complexity level may be
decreased.
[0101] In an embodiment, the amount by which the threshold to
demodulate the currently received symbol is changed may be
approximately expressed by applying a second order Taylor series,
or a higher order, to the exponential function based on the
comparison value.
[0102] FIG. 6 illustrates an example of a fixed threshold in a
method to adaptively set a threshold, in accord with an
embodiment.
[0103] Referring to FIG. 6, in the method to adaptively set a
threshold according to an embodiment, a training symbol having a
demodulation value of "0" and a training symbol having a
demodulation value of "1" are alternately received during a
predetermined training period. Because the training symbol having
the demodulation value of "0" and the training symbol having the
demodulation value of "1" are alternately received, a probability
distribution of the training symbol having the demodulation value
of "0" may be identical to a probability distribution of the
training symbol having the demodulation value of "1". Accordingly,
a fixed threshold 610 may be set to be an intermediate value
between "0" and "1". However, depending on characteristics of a
system, the probability distribution of the training symbol having
the demodulation value of "0" may differ from the probability
distribution of the training symbol having the demodulation value
of "1". Thus, the fixed threshold 610 may be changed from the
intermediate value between "0" and "1" to a value close to "0" or
"1". Also, the fixed threshold 610 may be set to be another value
depending on the characteristics of the system.
[0104] FIG. 7 illustrates an example of a threshold to demodulate a
currently received symbol.
[0105] Referring to FIG. 7, a fixed threshold 710 is set to be an
intermediate value between "0" and "1" based on a predetermined
training period. When a symbol having a demodulation value of "0"
or a symbol having a demodulation value of "1" is continuously
received, an output signal of ADC may not maintain an amplitude in
the symbol and, due to a DC fluctuation effect, may tend to have an
average value. Thus, when the symbol having the demodulation value
of "1" is continuously received, the output signal of the ADC may
have a tendency to decrease. When the symbol having the
demodulation value of "0" is continuously received, the output
signal of the ADC may have a tendency to increase. Accordingly,
when a received symbol is demodulated using the fixed threshold
710, the demodulation value may not be accurately determined.
[0106] According to an example embodiment, a threshold 720 to
demodulate a currently received symbol may be calculated using an
exponential function based on a comparison value obtained by
comparing a number of previously received symbols having the
demodulation value of "0" to a number of previously received
symbols having the demodulation value of "1". Accordingly, the
threshold 720 to demodulate the currently received symbol is
adaptively varied based on the comparison value. For example, when
the symbol having the demodulation value of "1" is continuously
received, the threshold 720 to demodulate the currently received
symbol may decrease. When the symbol having the demodulation value
of "0" is continuously received, the threshold 720 to demodulate
the currently received symbol may increase. In this instance, a
change in the output signal of the ADC resulting from the DC
fluctuation effect may be applied. Thus, when the received symbol
is demodulated using the threshold 720 to demodulate the currently
received symbol, the demodulation value of the received symbol may
be more accurately determined.
[0107] FIG. 8 illustrates an example of an apparatus 800 to set a
threshold, in accord with an embodiment.
[0108] Referring to FIG. 8, a demodulation value identifier 810
identifies a demodulation value of a previously received symbol
received during a predetermined symbol period.
[0109] A threshold setting unit 820 adaptively sets a threshold to
demodulate a currently received symbol based on the demodulation
value of the previously received symbol.
[0110] The apparatus 800 to set a threshold according to an example
embodiment may further include a buffer storing the previously
received symbol and the currently received symbol. The previously
received symbol and the currently received symbol stored in the
buffer are provided to the demodulation value identifier 810 and
the threshold setting unit 820.
[0111] Descriptions provided with reference to FIGS. 1 through 7
may be identically applied to the apparatus 800 to set a threshold
according to an example embodiment illustrated in FIG. 8 and thus,
repeated descriptions will be omitted for increased clarity and
conciseness.
[0112] The methods described above may be recorded, stored, or
fixed in one or more non-transitory computer-readable media that
includes program instructions to be implemented by a computer to
cause a processor to execute or perform the program instructions.
The media may also include, alone or in combination with the
program instructions, data files, data structures, and the like.
The media and program instructions may be those specially designed
and constructed, or they may be of the kind well-known and
available to those having skill in the computer software arts.
Examples of non-transitory computer-readable media include magnetic
media such as hard disks, floppy disks, and magnetic tape; optical
media such as CD-ROM discs and DVDs; magneto-optical media such as
optical disks; and hardware devices that are specially configured
to store and perform program instructions, such as read-only memory
(ROM), random access memory (RAM), flash memory, and the like.
Examples of program instructions include both machine code, such as
produced by a compiler, and files containing higher level code that
may be executed by the computer using an interpreter. The described
hardware devices may be configured to act as one or more software
modules in order to perform the operations and methods described
above, or vice versa. In accordance with an illustrative example, a
computer program embodied on a non-transitory computer-readable
medium may also be provided, encoding instructions to perform at
least the method described in FIG. 5.
[0113] The unit and apparatuses described herein may be implemented
using hardware components. The hardware components may include, for
example, controllers, sensors, processors, generators, drivers, and
other equivalent electronic components. The hardware components may
be implemented using one or more general-purpose or special purpose
computers, such as, for example, a processor, a controller and an
arithmetic logic unit, a digital signal processor, a microcomputer,
a field programmable array, a programmable logic unit, a
microprocessor or any other device capable of responding to and
executing instructions in a defined manner. The hardware components
may run an operating system (OS) and one or more software
applications that run on the OS. The hardware components also may
access, store, manipulate, process, and create data in response to
execution of the software. For purpose of simplicity, the
description of a processing device is used as singular; however,
one skilled in the art will appreciated that a processing device
may include multiple processing elements and multiple types of
processing elements. For example, a hardware component may include
multiple processors or a processor and a controller. In addition,
different processing configurations are possible, such a parallel
processors.
[0114] A number of examples have been described above.
Nevertheless, it should be understood that various modifications
may be made. For example, suitable results may be achieved if the
described techniques are performed in a different order and/or if
components in a described system, architecture, device, or circuit
are combined in a different manner and/or replaced or supplemented
by other components or their equivalents. Accordingly, other
implementations are within the scope of the following claims.
* * * * *